Alzheimer's disease (AD), a progressive degenerative disease of the brain primarily associated with aging, has become a more serious healthcare problem since its initial description almost a century ago (Alzheimer, A. Centralblatt fur Nervenheikunde und Psychiatrie, 1907, 30, 117-179). For example, the number of prevalent cases of AD continues to grow at an alarming rate of more than 5% annually in Japan (Citron, M. J. Neuroscience Research, 2002, 70, 373-379). Clinically, AD is presented by characterization of loss of memory, cognition, reasoning, judgment, and orientation. Motor, sensory, and linguistic abilities are also affected as the disease progresses until global impairment of multiple cognitive functions occurs. These cognitive losses take place gradually, but typically lead to severe impairment and eventual death in 4-12 years. Consequently, there is an urgent need for pharmaceutical agents capable of halting, preventing or reversing the progression of Alzheimer's disease.
β-Amyloid plaques (predominately an aggregate of a peptide fragment known as Aβ) and neurofibrillary tangles are two major pathologic characterizations associated with Alzheimer's disease. Patients with AD display characteristic β-amyloid deposits (β-amyloid plaques) in the brain and in cerebral blood vessels (β-amyloid angiopathy) as well as neurofibrillary tangles. Amyloidogenic plaques and vascular amyloid angiopathy also characterize the brains of patients with Trisomy 21 (Down's Syndrome), Hereditary Cerebral Hemorrhage with Amyloidosis of the Dutch-type (HCHWA-D), and other neurodegenerative disorders. Neurofibrillary tangles also occur in other dementia-inducing disorders (Varghese, J., et al, Journal of Medicinal Chemistry, 2003, 46, 4625-4630).
β-amyloid deposits are predominately an aggregate of Aβ peptide, which in turn is a product of the proteolysis of amyloid precursor protein (APP). More specifically, Aβ peptide results from the cleavage of APP at the C-terminus by one or more β-secretases, and at the N-terminus by β-secretase enzyme (BACE), also known as aspartyl protease, as part of the β-amyloidogenic pathway.
BACE activity is correlated directly to the generation of Aβ peptide from APP (Sinha, et al., Nature, 1999, 402:537-540), and studies increasingly indicate that the inhibition of BACE inhibits the production of Aβ peptide (Roberds, S. L., et al, Human Molecular Genetics, 2001, 10, 1317-1324).
Thus, based on the foregoing, it is clear that BACE inhibitors are useful, and development of new BACE inhibitors is highly desirable.